But if we—you and me—don’t deal with it, the awfulness won’t stop. It will get worse. It will spread further. It will last longer. It will get even harder to deal with.

What can we do? Lots. There is lots we can do. There is lots we need to do. But first we need to recognise the threat to all of us if we continue to fail.

Syria is the world’s biggest crime scene. It’s the crime of the century. And the crime wave has spread through the whole neighbourhood and beyond.

The scale of the crime in Syria is impossible to take in. When we turn to a crime novel for light relief, we read of one or two people being murdered, and the entire plot revolves around identifying and stopping the killer. In Syria, something like half a million people have been killed. One organisation alone has gathered names and details of over 209,000 individual civilians violently killed, with the vast majority, over 196,000, killed by the Assad regime and its allies.

Assad is the main killer. But because he and his allies have killed hundreds of thousands of ordinary adults and children, rather than just the one or two of a crime novel, we don’t get a neat detective story where he is tracked down and brought to justice. Instead of a police cell, he has a seat at the UN. Instead of a trial, he is cajoled to join in negotiations in Geneva. Instead of justice, he is offered bribes of billions of reconstruction money if only he will make a deal.

In a crime novel, why is it so important to catch the criminal? People die for all sorts of reasons—very few by murder. But crime threatens society more widely. Stopping crime, stopping killers, isn’t just about stopping a threat to a few individuals, it is about protecting an entire society from a breakdown in trust.

To prosper, a society needs trust. For our everyday dealings with each other to run smoothly, we need to be able to trust that we are not all out to rob or injure each other. And when someone violates that trust, we need to know we can rely on each other to stop them from repeating that violation.

International relations similarly require trust. Without trust we are unable to travel, unable to trade over any distance. Without trust we face piracy, plunder, and war.

There will always be some violations of trust in international relations as within nations’ own societies. Maintaining trust depends on sincere collective efforts to counter those violations.

The failure on Syria has torn an enormous hole in that international trust. Governments cannot trust governments that are openly opposed to them, but now also find they cannot trust governments that are supposed to be their allies. And the international lack of trust then spreads into national societies with heightened xenophobia and extremism.

The unravelling goes like this: Assad sees himself free to shoot, torture, bomb and poison Syrian men, women, children, by the thousands. International governments show themselves unwilling to join in collective action to stop him, judging the risk too great. UN resolutions and all the other instruments of diplomacy are revealed as a sham.

And as governments find it easier to tolerate Syrians being murdered in Syria than to stand together against Assad, why not tolerate them drowning in the Mediterranean? The judgement is similar: the political risk of uniting in offering safe passage is deemed too great.

Then the same applies when we reach Europe’s shore: brutality triumphs over unity. If murder abroad and drowning offshore is acceptable, how different is it inside Europe’s borders?

In Europe, instead of an effective collective humanitarian response, we’ve had separate states fracturing into individual responses of varying degrees of brutality. This hasn’t just harmed Syrians arriving to Europe, it continues to harm European societies. If a Syrian could be beaten, or robbed, or detained without charge in a European country yesterday, who else can be beaten or robbed or detained in that country today? And which country will it happen in tomorrow?

This unravelling of trust has gone so far that we risk losing sight of where it begins. It has gone on so long we risk believing this is how the world must be.

So what can we do? First, recognise that crimes on the scale seen in Syria are not an internal issue but an international threat. They threaten all of our societies and all of humanity. They threaten us, our friends, our families, our children. Stopping these crimes in Syria is a matter of self defence.

Second, understand that we may need to use force. The UK and other states accept the need to use force against international non-state criminal threats in Syria: against Al Qaeda and ISIS. The Assad regime is equally an international criminal threat, even though it clings to the trappings of a state.

Third, understand that to restore trust we have to protect civilians. Assad’s crime is the mass slaughter of civilians, and the deliberate destruction of any civil society outside the control of the regime. Merely prosecuting a few individuals at some future date will not restore trust either within Syria or internationally.

Protecting civilians is not a simple task for today or tomorrow. It requires long term commitment to protecting Syrian lives and protecting and supporting independent Syrian civil society. It requires showing trust and earning trust, not a hit and run action followed by handover to the next authoritarian offering security in exchange for an arms deal.

We have so far failed on Syria because of individual and collective failures of comprehension, of imagination, of morality, and of courage. Changing that is not just a task for leaders; it is a task for all of us in understanding our own personal stake in the outcome of Syria’s crime story.